94 lines
3.7 KiB
C++
94 lines
3.7 KiB
C++
// Copyright 2020 Google LLC.
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// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
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#include "tools/fiddle/examples.h"
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REG_FIDDLE(SkPath_arcto_conic_parametric2, 512, 512, false, 0) {
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/** Add a weighted quadratic bezier from the last point, approaching control point
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(x1,y1), and ending at (x2,y2). If no moveTo() call has been made for
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this contour, the first point is automatically set to (0,0).
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If the starting point is (x0, y0), then this curve is defined as the
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paramentric curve as `t` goes from 0 to 1:
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s := 1 - t
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x := ((s * s * x0) + (w * 2 * s * t * x1) + (t * t * x2)) /
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((s * s) + (w * 2 * s * t) + (t * t))
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y := ((s * s * y0) + (w * 2 * s * t * y1) + (t * t * y2)) /
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((s * s) + (w * 2 * s * t) + (t * t))
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@param x1 The x-coordinate of the control point on a quadratic curve
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@param y1 The y-coordinate of the control point on a quadratic curve
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@param x2 The x-coordinate of the end point on a quadratic curve
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@param y2 The y-coordinate of the end point on a quadratic curve
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@param w The weight of the control point (x1,y1)
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*/
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SkPoint conic(SkPoint p0, SkPoint p1, SkPoint p2, float w, float t) {
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float s = 1 - t;
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return {((s * s * p0.x()) + (2 * s * t * w * p1.x()) + (t * t * p2.x())) /
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((s * s) + (w * 2 * s * t) + (t * t)),
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((s * s * p0.y()) + (2 * s * t * w * p1.y()) + (t * t * p2.y())) /
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((s * s) + (w * 2 * s * t) + (t * t))};
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}
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void draw(SkCanvas* canvas) {
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canvas->clear(SkColorSetARGB(255, 255, 255, 255));
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SkPaint paint;
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paint.setAntiAlias(true);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setStrokeWidth(1);
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SkPoint center = {256, 256};
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float r = 192;
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SkRect oval = {center.x() - r, center.y() - r, center.x() + r, center.y() + r};
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canvas->drawOval(oval, paint);
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float startAngle = 15;
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float sweepAngle = 75;
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SkPath arc;
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arc.arcTo(oval, startAngle, sweepAngle, false);
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SkPaint arcPaint(paint);
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arcPaint.setStrokeWidth(5);
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arcPaint.setColor(SkColorSetARGB(255, 0, 0, 255));
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canvas->drawPath(arc, arcPaint);
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SkPaint pointPaint;
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pointPaint.setAntiAlias(true);
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pointPaint.setStrokeWidth(8);
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pointPaint.setStrokeCap(SkPaint::kRound_Cap);
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pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
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float finalAngle = startAngle + sweepAngle;
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float middleAngle = startAngle + 0.5f * sweepAngle;
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float weight = cos(SkDegreesToRadians(sweepAngle) / 2);
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SkPoint p0 = {r * SkScalarCos(SkDegreesToRadians(startAngle)),
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r * SkScalarSin(SkDegreesToRadians(startAngle))};
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float d = r / weight;
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SkPoint p1 = {d * SkScalarCos(SkDegreesToRadians(middleAngle)),
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d * SkScalarSin(SkDegreesToRadians(middleAngle))};
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SkPoint p2 = {r * SkScalarCos(SkDegreesToRadians(finalAngle)),
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r * SkScalarSin(SkDegreesToRadians(finalAngle))};
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p0 += center;
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p1 += center;
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p2 += center;
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canvas->drawLine(p0.x(), p0.y(), p1.x(), p1.y(), paint);
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canvas->drawLine(p1.x(), p1.y(), p2.x(), p2.y(), paint);
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const int N = 16;
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for (int i = 0; i <= N; ++i) {
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SkPoint p = conic(p0, p1, p2, weight, (float)i / N);
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canvas->drawPoint(p.x(), p.y(), pointPaint);
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}
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pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0));
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canvas->drawPoint(p0.x(), p0.y(), pointPaint);
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canvas->drawPoint(p1.x(), p1.y(), pointPaint);
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canvas->drawPoint(p2.x(), p2.y(), pointPaint);
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SkPath weightedQuadratic;
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weightedQuadratic.moveTo(p0);
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weightedQuadratic.conicTo(p1, p2, weight);
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paint.setColor(SK_ColorYELLOW);
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paint.setStrokeWidth(2.5);
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canvas->drawPath(weightedQuadratic, paint);
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}
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} // END FIDDLE
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